1. Field of the Invention
The present invention relates to a reflective Ag alloy film for reflectors and to a reflector comprising the same. Specifically, it relates to a reflective Ag alloy film for reflectors which has a high reflectivity and rarely experiences a reduction in reflectivity by heating and to a reflector comprising the same.
2. Description of the Related Art
An Ag film has been used for many purposes as it has a high reflectivity for visible light. For example, it is used for reflectors for automotive lamps, backlights for liquid crystal displays, reflectors for lighting devices, mirrors for optical parts and reflectors for light emitting parts such as LED's. A reflector comprising an Ag film is manufactured by coating a glass or resin substrate with Ag by sputtering or the like, and the Ag film is thus used as a reflective film for reflectors.
However, the Ag film is unsatisfactory in terms of environmental durability. As it is deteriorated by moisture, it is difficult to use it for a long time. Further, Ag is easily diffused by heating at 100 to 200° C. and the cohesion of Ag occurs, thereby reducing its reflectivity.
Therefore, it is proposed to increase its chemical stability by adding various precious metals to Ag as shown in JP-A 2001-226765 (patent document 1) . Although the chemical stability under a wet environment is increased in this method, the average surface roughness of the film is deteriorated by a rise in temperature caused by radiation from a lamp. Therefore, the improvement of durability is not attained yet and a problem to be solved for its practical use still remains.
The formation of a transparent protective layer on an Ag film is effective in improving its durability. An organic resin or metal oxide shown in JP-A 2000-106017 (patent document 2) is generally used in the protective layer. Even when the Ag film is coated with these, an organic resin film involves a problem such as light absorption by the protective layer and a reaction with a component of the protective layer, and a metal oxide film has a problem that deterioration is caused by a defect such as a pin hole.
[patent document 1] JP-A 2001-226765
[Patent document 2] JP-A 2000-106017